The present invention relates generally to magnetic resonance imaging (MRI), and more particularly to, a pulse sequence, method, and apparatus for multi-slice acquisition imaging to acquire black blood contrast images during successive R-R intervals of a cardiac cycle.
MRI uses radio frequency pulses and magnetic field gradients applied to a subject in a strong homogenous magnetic field to produce viewable images. When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, MZ, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (GxGy and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
Current techniques for the acquisition of Fast Spin Echo (FSE) images with enhanced black blood contrast are limited to acquiring data in every other heartbeat. Acquiring data in this manner allows the magnetization to relax between successive inversions. For a typical cardiac examination having 256 readout points, 192 phase encodes, a three-quarter phase FOV, and an echo train length (ETL) of between 12 to 16 echoes, the scan time is typically 18 to 24 heartbeats or R-R intervals. In order to minimize respiratory artifacts, the images are acquired during an end-expiratory breath-hold. In order to achieve sufficient coverage, typically, 8 to 12 contiguous slices are acquired in successive breath-holds, which may be exhausting for the patient undergoing the MR study. Additionally, since data is acquired in alternating heartbeats, the data acquisition process is extended which negatively affects patient throughput.
It would therefore be desirable to have a technique to acquire black blood contrast images with improved acquisition for efficient imaging that is capable of imaging in successive heartbeats or R-R intervals. It would also be desirable to acquire multiple slices of MR data in each heartbeat so as to shorten data acquisition time and increase patient throughput.